Working with RAW images

Tutorial: Raw

Working with raw images

Your EOS camera captures images in a 'raw' format. This is neither an abbreviation nor a technical term. It simply means 'not processed'.The raw data comes from the millions of pixels that make up the camera sensor. Each pixel is photosensitive and responds to light by generating a small electric current. The value of each current is converted to a digital format. This mass of data forms the bulk of the raw image file.

This tutorial will explain how you can use these raw files to refine the decisions you made when you took the original photo.

  • Raw vs. JPEG
  • Canon Digital Photo Professional (DPP)
  • Navigating DPP
  • Brightness
  • White balance
  • Picture Style
  • Contrast
  • Color tone
  • Color saturation
  • Sharpness
  • Saving Images

TBC

JPEG vs. raw

JPEG is an abbreviation and used to describe a method of reducing the large amount of data captured by the camera to a smaller file. It does this by checking various settings on the camera, such as white balance, Picture Style, Contrast, Color saturation, Color tone and Sharpness. The camera processes the image according to these values and discards all the information not required. A JPEG image is also compressed which reduces the size of the file when it is saved, but allows it to open to a larger size when viewed

Make the most of wide angled lenses

An advantage of shooting JPEG files is that the images can be printed, transmitted or saved without any further work. The disadvantage is that you have limited ability to change the image once it is taken.

Many photographers prefer to shoot and save raw files. Here, all the data from the sensor is saved with minimal processing. The advantage of a raw file is that you can make many of the shooting decisions when the image is opened on a computer.

If you shoot a JPEG file in Daylight with the white balance set to Tungsten, it is a major problem. With a raw file you select the white balance after the exposure, so it is no problem at all. There are many other characteristics you can change and adjust, giving more control over the image than you had at the time of shooting

Canon Digital Photo Professional (DPP)

To process a raw file you will need software (a raw converter) such as Canon's Digital Photo Professional (DPP) which is included on the software CD supplied with EOS and PowerShot G cameras.

In addition to all the captured data, the raw file also includes information about the camera settings at the time of the exposure. When you convert an image with DPP, it will open with these settings applied - but you can change them.

Once you have made all the changes, you can 'Convert and save' the image. This will give you a choice of JPEG or TIFF file, but the original raw file remains unchanged. This means you can go back and open it again to create an image with different characteristics.

Navigating DPP

The navigation and use of DPP is straightforward; here is a simple guide to help you understand the structure. Click a folder containing image files to display them in the DPP window. Then click one of the images to select it.

Take a look at the buttons along the top of the window. Click 'Edit image window' (far left) to enlarge the selected image. Then click 'Tool Palette' (third from left) to bring up the panel of controls. Check that the 'RAW' tab is selected at the top of the palette.

Brightness

The Brightness slider at the top of the palette lightens or darkens the image (as shown below).

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The feature can be used to overcome smaller exposure errors, though the result is not exactly the same as getting the exposure right in the first place. The button with the curved arrow takes you back to the original setting.

White balance

White balance aims to match the colour sensitivity of the sensor to the colour temperature of the light falling on the subject. Colour temperature changes during a day as well as under cloudy skies or in the shade.

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The drop-down menu on the palette matches the white balance settings on the camera - Daylight, Shade, Cloudy, Tungsten, White fluorescent light, Flash and Color temperature. Sometimes the changes are subtle - the Cloudy setting above is a little warmer than the Daylight setting.

The centre of this image has been enlarged using the 50% button from the menu so that the result can be seen more effectively. The enlargement is lost when the image is saved. However, you can crop the image using the 'Trimming Angle' button (second from right) and save the cropped image.

Picture Style

Picture Style parameters include contrast, hue, saturation and sharpness.

A Picture Style can also include subtle changes to a single colour, making blues lighter, or creating a more vivid red. Some Picture Style settings are aimed at specific subjects - Landscape or Portrait, for example. Others are more general - Standard, Faithful, Neutral, for example. Before you shoot it is sometimes difficult to know which Picture Style will best suit the subject. With DPP and a raw file you can delay the decision until the image is on your computer screen and then experiment.

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As you select a different Picture Style from the drop-down menu, the image will change immediately to show you the effect. The video above show the use of Neutral and Portrait Picture Styles.

Flash

As you select a different Picture Style from the drop-down menu, the image will change immediately to show you the effect. The video above show the use of Neutral and Portrait Picture Styles.

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Picture Style can affect just a small range of colours in an image. As a comparison, here is the same image with a colour temperature setting of 8000 K. This has given an overall warmth to the image, rather than just affecting the colours of the face.

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Picture Style is also the place to experiment with monochrome images. Once you have selected the Monochrome style you can experiment with brightness and other settings to produce the effect you are looking for.

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Contrast

The contrast slider can increase the impact of a subject with flat tones. As with all these adjustments, you see the change immediately and can experiment with different values.

FLASH

In addition to contrast, you can adjust the highlight and shadow values to show more or less detail in these areas. Adjusting both values creates the result below.

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Color tone

The variations available from the Color tone slider can be similar to those of White balance and Picture Style. However, there are times when Color tone adjustment gives the results you want. This video shows the Color tone set to 0, +4 and -4.

Color saturation

Color saturation is one of the Picture Style parameters, but has its own slider in the Tool Palette. As you can see from this video (0, +4 and -4), it increases the vibrancy of the colours.

Sharpness

Sharpening of images is often important for images. The effect of sharpening is actually more like increasing contrast selectively. The video below show the difference between no sharpening and maximum sharpening. The 200% button has been selected from the menu to select a part of the image where the effect is most noticeable.

Saving images /h3>

Once you have made all the changes required, go to the main DPP menu (not the buttons in the window), select 'File', then 'Convert and save…'. This will give the window below, where you can select the type of file you want to save. Options include JPEG and TIFF, or both together. The 'Image quality' slider sets the level of file compression - lower values are good for computer display, higher values are better if you plan to print the image (though the file size will be larger).

he 'Output resolution' is shown in dpi which stands for Dots Per Inch. The dpi is a measure of the resolution of an image when it is printed or displayed on a monitor. A dpi of 350 is good for printing - 72dpi is adequate for a computer display. Remember that you are not committing to anything with this save - you can always go back to the raw file and start again to produce the same or a different image.

When you quit DPP it will ask if you want to save edited images (above). This is very different to the 'Convert and save…' option. Here, DPP is simply attaching the changes you have made to the raw image. These changes will be applied to the raw image the next time it opens. There is no change to the raw image itself, only to information linked to the image. This feature is very useful if you need to spread your modification work over two or more sessions - you do not have to start from the beginning each time.

Experiment with DPP

The best way to learn how to use DPP is to use it. Every change you make is shown on screen in real time. None of the changes affect the raw image, so you can always go back and start over. However, we will be looking at more of the many DPP features in the future.

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